This invention generally relates to motor-compressor units, and more specifically to motor-compressor units employing a yoke and a slide block to transmit motion from a compressor crankshaft to a pair of opposed compressor pistons, and to a yoke and slide block combination especially well suited for use in certain motor-compressor units.
The utilization of hermetically and semi-hermetically sealed motor-compressor units has become increasingly prevelant in recent years, particularly in refrigeration applications where the motor-compressor units are employed to compress refrigerant vapor. Typically, a motor-compressor unit includes a compressor, a motor, and a shell enclosing both the compressor and the motor; and the compressor, in turn, includes a rotatable crankshaft and a plurality of pistons, with each piston connected to the crankshaft via a conventional wrist pin and connecting arm. In operation, the shell is filled with low pressure suction vapor, the motor is employed to rotate the compressor crankshaft, and rotation of the crankshaft reciprocates the compressor pistons via the wrist pins and connecting arms. Reciprocating movement of the compressor pistons draws the low pressure vapor into the compressor, compresses the vapor, and then directs the vapor into a high pressure discharge line that conducts the compressed vapor from the compresor and through the shell of the motor-compressor unit.
While these conventional prior art motor-compressor units operate very satisfactory under a wide variety of circumstances, efforts have continuously been made to improve the efficiency of motor-compressor units, and recently these efforts have resulted in the design of a revolutionary new type of motor-compressor unit having, inter alia, a large central region which, during operation, is filled with high pressure, compressed vapor. During the development of this new motor-compressor unit, it was learned that when the conventional wrist pin-connecting arm arrangement is used to connect the compressor pistons with the compressor crankshaft, under certain circumstances, the wrist pins are not lubricated as easily as or to the extent desired. For this reason, the new type of motor-compressor unit is provided with a yoke and a slide block to connect and to transmit motion from the compressor crankshaft to the compressor pistons.
Providing the new type of motor-compressor unit with prior art yoke-slide block arrangements, however, involves a perplexing dilemma. To elaborate, to reduce the cost and improve the performance of the motor-compressor unit, it is desirable to use a comparatively small, low mass yoke; and this may be done by employing a yoke having two, opposed, closed longitudinal sides and two, opposed, open transverse sides. In assembly, the compressor pistons are connected to the closed sides of the yoke and a slide block is supported by the yoke for longitudinal movement through the open sides thereof. Such a yoke, often referred to as an open yoke, does not limit longitudinal movement of the slide block, allowing the use of a compact, light weight yoke.
With the new type of motor-compressor unit outlined above, the high pressure vapor in the central region of the motor-compressor unit urges the compressor pistons outward. When prior art open yokes are employed with this new type of motor-compressor unit, the forces urging the pistons outward tend to bend the closed sides of the yoke outward. This bending may cause the pistons connected to the yoke to bind against adjacent surfaces of the compressor, increasing the frictional forces therebetween and otherwise adversely affecting performance of the motor-compressor unit. Of course, this bending can be inhibited by employing a yoke having four closed sides or by employing a more massive, stronger yoke; but doing this increases the size, inertia, and cost of the yoke.